The invention is directed to a wet collector apparatus to separate or assist in the separation of particulates from aerosols. Particulates, as dust, mist and fumes, vary in size and are usually insoluble. An overall particle range susceptible to wet collection varies from 0.2 to greater than 10 microns. Dusts are usually at least 1 micron, mists at least 10 microns, and fumes less than 1 micron in size. Wet collectors vary in design and use one or several mechanisms for both conditioning of the particulate and disengaging it from the carrier gas. The effectiveness of the wet collector is dependent upon the degree of interaction it can produce between the dispersed liquid droplets and the particulate.
One type of wet collector is a Venturi scrubber having a Venturi-type constriction through which the carrier gas passes. The Venturi constriction is provided by converging the walls of the inlet to the scrubber. These walls have fixed slopes and form a Venturi throat having a fixed width and length. Venturi structures having variable width throats have been used. These structures have longitudinal dampers movably mounted on the converging walls to vary the width of the Venturi throat. The long longitudinal dampers are moved to change the width of the throat and fluid flow characteristics of the throat. The longitudinal dampers change the angles or slopes of the walls forming the throat, thereby changing the effective slopes of the side walls which alters the efficiency of the structure and causes turbulence in the gas flow. Also, the large longitudinal dampers are difficult to move and hold in adjusted positions.
A scrubbing liquid, usually water, is introduced into the gas flow at or near the constriction of the Venturi. The high gas velocities atomize the scrubbing liquid and the turbulence created leads to increased high collection efficiencies for sub-micron particles as the energy input is increased. The Venturi scrubber functions on the basis of several collection mechanisms. These mechanisms include impingement which results when a particle and droplet collide. In the sub-micron size Brownian movement becomes significant. The Brownian movement and turbulent coagulation are factors which facilitate agglomeration of the particles. Turbulent coagulation results when a velocity gradient is present in an aerosol because particles moving at different velocities in adjacent streams tend to collide.
The energy required to perform the scrubbing action in a Venturi scrubber results in Venturi pressure drop. Scrubbing efficiency is generally a function of this pressure drop. The higher the pressure drop, the higher the removal efficiency of sub-micron particles. The pressure drop required for efficient scrubbing will vary with the particle size of the specific dust, fume or mist to be removed and the overall scrubbing efficiency required. Increasing the inlet gas velocity and/or water jet rate increases the Venturi pressure drop. It is desirable to control the pressure drop to provide for variations in particulates and gas flow.